1. Statement of the Technical Field
The inventive arrangements are directed to the field of power converters, and more particularly, to power converters including self-driven synchronous rectifiers.
2. Description of the Related Art
Although many types of DC-DC converters have been traditionally implemented using diode-based designs, many conventional DC-DC converters use metal-oxide-semiconductor field effect transistor (MOSFET) based rectifier circuits. MOSFET-based rectifier circuits improve the efficiency of DC-DC converters by reducing the power dissipated in the output rectification stage by reducing the output voltage drop in the rectification stage.
Typically, DC-DC converters can be operated in one of two modes, continuous and discontinuous. Discontinuous mode converters are typically used in low power applications. In general, discontinuous mode converters require that the current in the transforming element on the secondary side fall to zero prior to the end of a switching cycle. This operation is typically accomplished by utilizing switching elements to open or close the circuits in the input and output sides of the power converter. For example, in the case of a synchronized MOSFET rectifier coupled to the secondary winding of a transformer, the signal to the gate of the MOSFET rectifier can be switched on or off, depending on whether the primary or the secondary winding of the transformer should be currently conducting current.
Typically, synchronized MOSFET rectifiers in DC-DC converters are controlled using self-driven and control driven techniques. However, such techniques typically fail to prevent current spikes, or cross-conduction, as the current switches from one side of the DC-DC converter to the other. For example, some self-driven synchronous rectifier designs connect the gate of the MOSFET rectifier directly to the secondary winding of the transformer, resulting in low MOSFET driving losses. However, because the driving voltage and timing for the synchronous MOSFET rectifier is highly dependent on the converter topology, the useable input voltage range is limited because the gate drive voltage varies with input voltage. Control-driven techniques, though more complex than self-driven methods, can overcome some of these limitations, except for preventing cross conduction. Furthermore, control-driven techniques typically require an additional circuit, external to the rectifier circuit, such as a control integrated circuit. Therefore, control-driven techniques can offer constant gate drive voltage but have driving losses and additional cost because of added parts.